Understanding the Stack Effect in Your Home

Stack Effect In Your Home

If you never spend time in your basement or crawl space, you don’t have to worry about the accumulation of moisture, right? Well, not necessarily…  

Crawl spaces and basements are well known for being damp, dank spaces. Even when your home has no flooding issues and has perfect plumbing, these underground spaces can have a lot of moisture issues. One major culprit for humidity in your home is a phenomenon called the "stack effect." 

As a homeowner who wants to avoid humidity and mold growth in their home it is important to understand the “stack effect” and why it matters for your home.  

What is the stack effect? 

stack effect

The stack effect refers to the process in which hot air leaves the home through your attic and upper levels. As it does, a vacuum is created below, and new air is pulled upwards through the basement, crawl space, and lower levels. 

Basements and crawl spaces are naturally cooled by the earth around them, which keeps a relatively constant temperature year-round. Depending on the season, the air inside your basement or crawl space will either be warmer or cooler than the air outside. During winter months, warmer air will enter the basement, crawl space, or lower level and exit through the attic or upper levels.  

In the summer, the stack effect is reversed. Warmer air enters through the attic and upper levels, cools, and then travels down and out of the basement, crawl space, or lower level. 

How the stack effect can lead to humidity and mold 

Mold on beasement wall

Imagine this: It is an 80°F (27°C) day with 80% relative humidity. The higher the relative humidity number is, the closer the air is to becoming "full" of water. Warm air holds the most water, and as it cools and "shrinks", it can hold less water. The relative humidity number shows how much humidity is in the air relative to how much it can hold. Air at 80% relative humidity is 80% "full" of water. When the humidity rises above 100% outside, it rains. Picture that humid air moving into your crawl space or basement. This cool, underground space drops the temperature of the air to 68°F (20°C). Because of this, the relative humidity goes up, even if no new water is added to the air. This is because for every 1°F the temperature drops, the relative humidity of the air will rise by 2.2%. 

In this case, the relative humidity will rise by 26.4% (12°F x 2.2%). Add the 80% humidity you already had, and you have 106.4% relative humidity. However, when the humidity reaches 100%, the air can hold no more water! So, this extra humidity is dropped from the air as condensation, which is deposited on cool surfaces in the space, such as wood, metal, or concrete. 

Moisture inevitably leads to mold growth. With the stack effect constantly circulating air throughout your home, this air also disperses mold spores, humidity, and odors. As humidity settles in your home, the likelihood of mold increases significantly. 

Mold spores and your home  

As mold reproduces, it releases millions of allergenic mold spores into the air. As mentioned in our Mold and Dust blog, mold can begin to grow in a wet basement in as little as 24-48 hours, with 1 billion mold spores growing on a single square foot of drywall. 

Time Magazine reports that there can be hundreds of thousands of mold spores in a single cubic meter of air, and a person inhales 10-12 cubic meters of air each day.

Mold Spores in air

Because of the stack effect, these mold spores will not be confined to your basement or crawl space. As air moves up from these spaces into your home, it will bring mold spores and humidity along with it.  

If you notice that you suffer from symptoms such as a runny nose, watery eyes, mild allergic reactions, a scratchy throat, fatigue, or headaches at home that seem to disappear once you leave the building, mold allergens may be the culprit. 

Of course, mold and rot will also wreak havoc on your home. Damaged wood, structural issues, and ruined personal property are all consequences of mold, mildew, rot & humidity in a basement or crawl space. 

How to control humidity and mold in your basement or crawl space 

So how can you control the humidity and mold in your basement or crawl space?

TripleSafe Pump System

Thrasher Foundation Repair TripleSafe Pump System

  1. Install a sump pump Whether you have experienced water issues in your basement or not, safeguarding your home with our reliable sump pump will help you manage moisture levels in your home.
  2. Invest in a dehumidifier Dehumidifiers extract excess moisture from the air helping to reduce humidity levels in your basement. This creates a drier, less favorable environment for mold growth.
  3. Foundation repair or professional waterproofing Foundation cracks can allow for water to seep into your basement or crawl space. This creates a damp environment, perfect for mold growth. By repairing your foundation and properly waterproofing these spaces you will reduce the chances of encountering mold in your home.
SaniDry Sedona Panel

The world's most efficient high-performance dehumidifier and filtration system and in a small size to take up less space in your basement or fit in small crawl spaces. 

The key to controlling mold in your basement or crawl space is to eliminate the humidity that keeps it thriving. At Thrasher, we recommend starting by sealing off any vents, covering any exposed dirt and concrete, and installing airtight crawl space doors. Replacing drafty basement windows will also help hold back outside air. 

By keeping your basement or crawl space dry and controlling humidity levels the risk of mold infestation lessens, protecting both your property and your health.

When in doubt, talk to the experts 

Hey there, we are the friendly team at Thrasher Foundation Repair, and excited to meet you. With nearly 50 years of experience in foundation repair and basement solutions we've got you covered when it comes to basements and crawl spaces. 

If you happen to live in or around Omaha, Kansas City, Wichita, Denver, Springfield, Grand Island, Sioux City, or Peoria, we're here to help with any basement questions, humidity issues, or hey, even just chatting about life – we’re up for that, too. You can reach out to us by calling us at 1-844-948-3306, filling out this form, or starting a chat in the bottom right-hand corner.


Article Categories:

Related resources

5 Effective Tips To Reduce Humidity In Your Basement

February 29th, 2024

5 Effective Tips To Reduce Humidity In Your Basement

Discover 5 effective ways to reduce humidity in your basement, keeping it dry and comfortable. Learn practical tips for a...

Read more
The Ultimate Guide: Prevent Basement Flooding in Colorado

February 22nd, 2024

The Ultimate Guide: Prevent Basement Flooding in Colorado

Colorado Basements: How To P

Read more
Does Your Crawl Space Affect The Air Quality In Your Home?

October 30th, 2023

Does Your Crawl Space Affect The Air Quality In Your Home?

Discover the hidden connection between your crawl space and indoor air quality in this blog. Learn how addressing crawl space...

Read more
Fall Pest Prevention: 7 Expert Tips to Keep Your Home Pest-Free

October 12th, 2023

Fall Pest Prevention: 7 Expert Tips to Keep Your Home Pest-Free

As the fall season brings comfy sweaters, pumpkin spice, and spooky movies, it also invites unwanted pests into your cozy...

Read more